Should I be worried?

So I have been with my boyfriend for 5 months now. I was at his house and we were looking through a bunch of his stuff. In the box, it had pictures of us, little keepsakes from previous dates, love letters i would send to him. But one thing that kind of bothers me is that he still has stuff from his ex. Like in the same box. Photographs of them together. I even saw one with them kissing. He has mentioned her a couple of times. In his defense, I would initiate those conversations because i am all about learning from mistakes. I know that he dated her for a little over a year. So should I be worried that he still keeps these things of her?